APLN and atrial fibrillation: Taken together, these findings indicate for the first time to our knowledge that reduced atrial-specific apelin bioavailability in the fibrillating atrial myocardium contributes to enhanced atrial oxidative stress, removes an endogenous mechanism to maintain normal atrial CV, and, thus, may play an important role in the vulnerability and treatment of atrial oxidative injury and electrophysiological remodeling observed in patients with AF.